As a process for obtaining a high molecular weight polyketone which exhibits with a high mechanical thermal property, EP Patent No. 319083 discloses a process of polymerization at a lower temperature, using a catalyst comprising palladium, 1,3-bis[di(2-methoxyphenyl)phosphino]propane and anion. Another method using a catalyst comprising palladium, 2-(2,4,6-trimethylbenzene)-1,3-bis[di(2-methoxyphenyl)phosphino]propane and anion is disclosed in JP-A No. H4-227726. JP-A No. H5-140301 discloses another process using a catalyst comprising palladium, 2-hydroxy-1,3-bis[di(2-methoxyphenyl)phosphino]propane and anion. By any of these processes, however, a yield of the polyketone obtained per a catalyst is low and it is difficult to synthesize a phosphor ligand and those processes are costly, thereby it being economically problematic.
As a process of obtaining a high molecular weight polyketone using an inexpensive catalyst, a process comprising performing polymerization in a solvent of tert-butanol using a catalyst comprising palladium, 1,3-bis(diphenylphosphino)propane and an anion of boron-based fluorides is disclosed in JP-A No. H6-510552. High molecular weight polyketone is obtained in this process, but the yield of the polyketone obtained per a catalyst is very low, and as a result the cost of polyketone is increased, thereby it being problematic.
As a process for obtaining a high molecular weight polyketone economically, a process comprising performing polymerization in a mixed solvent of methanol and 1 to 50 vol % of water is disclosed in JP-A No. H8-283403. In this process, a catalyst comprising a Group 10 element such as palladium, 1,3-bis(diphenylphosphino)propane and an anion of an inorganic acid is used. In particular, in the case of using palladium acetate, 1,3-bis(diphenylphosphino)propane and phosphotungstic acid in a solvent of methanol with 17 vol % of water, a polymer with an intrinsic viscosity of 1.36 is obtained at 85° C. at 4.8 MPa of an equimolar mixed gas of ethylene and carbon monoxide for 30 min. At that time, catalytic activity is 5.7 kg/g-Pd·hr. If sulfuric acid is used for the mixed solvent, instead of phosphotungstic acid, catalytic activity is 9.5 kg/g-Pd·hr. According to this process, due to high catalytic activity, relatively high molecular weight polyketone is obtained, but even with a longer polymerization time, it would be impossible to obtain a polymer with intrinsic viscosity of 2 or more, which is required to be used as a high performance material.
EP Patent No. 0361584 discloses a process comprising performing polymerization at a lower pressure using palladium, 1,3-bis(diphenylphosphino)propane and trifluoroacetic acid. According to this process, a polymer with catalytic activity of 1.3 kg/g-Pd·hr, and intrinsic viscosity of 1.8 can be obtained by polymerization at an input ratio of 1:2 of ethylene and carbon dioxide at 50° C. and at 4 MPa for 5.2 hours. By this process, a polyketone can be obtained at relatively low temperature and low pressure, but it is be impossible to obtain a polymer with high intrinsic viscosity, which is required to be used as a high performance material.
JP-A No. 2002-317044 discloses a method of using sulfuric acid as an inorganic acid in a catalyst system which is similar to those in the prior art. In this process, polymer with an intrinsic viscosity of 6.45 is obtained by polymerization of a Group 10 element such as palladium and 1,3-bis(diphenylphosphino)propane in a solvent of methanol at 80° C. at 5.5 MPa of an equimolar mixed gas of ethylene and carbon monoxide for 30 min. At that time, catalytic activity is 6.0 kg/g-Pd·hr.
Under these conditions, in a process of preparing polyketone using carbon monoxide and an ethylenically unsaturated compound, there is real demand for developing a technique for preparing polyketone having high catalytic activity as well as high intrinsic viscosity suitable for a tire cord.
In order to solve the above-mentioned problems, it is an object of the present invention to provide a process for preparing polyketone, with improved catalytic activity and intrinsic viscosity for a shorter polymerization time, by using a mixed solvent of 40 to 60 mol % acetic acid and 40 to 60 mol % water, as a liquid medium, and the precursor of palladium chloride compound 1,3-bis[di(methoxyphenyl)phosphino]propane, as a catalyst.